Hydrocarbon bearing diatomite formations are unique because they often have high oil saturation and high porosity, but have little permeability, i.e., they contain significant amounts of oil but few flow channels or fractures through which oil could flow and, ultimately, be recovered. The unique properties of this type of formation arise because of its morphology. The formation is composed largely of skeletal remains of diatoms. These skeletons and their fragments are hollow and fluids may flow only through natural micropores and through fractures and openings resulting from skeletal decrepitation.
Oil recovery from diatomite formations is usually quite limited because a significant portion of oil saturation may be bypassed using conventional production techniques such as cyclic or drive steaming. Significant improvement of oil recovery would require that a method of displacing oil from the interior of the diatoms into the flow channels between the diatoms be provided. Furthermore, it would be necessary to improve permeability in the natural flow channels so that the oil can be recovered.
Various methods have been proposed for increasing crude oil production from diatomite formations. For Example, U.S. Pat. No. 4,485,871 (assigned to the assignee of this application) teaches a method of recovering hydrocarbons from diatomite in which an alcohol is injected into the formation followed by an aqueous alkaline solution. However, it has been found that certain formations do not respond to this type of stimulation. In particular, oil recovery using this method is not optimum in formations which are deeply buried and have not been extensively exposed to the atmosphere or oxygen bearing formation water. The interfacial tension and oil/rock wettability in these deeply buried formations must be modified in order to enhance oil recover. A related method is described in U.S. Pat. No. 4,374,023, also assigned to the assignee of this application.
U.S. Pat. No. 4,167,470 teaches an alternative method of recovering oil from diatomite in which a hydrocarbon solvent is contacted with mined diatomite ore in a 6 stage extraction process. Solvent is then recovered in a steam stripping apparatus. There are several problems in utilizing this process in a cost effective manner. For example, the ore must be mined, with the attendant environmental and economic considerations. Furthermore, the process is extremely complex and capital intensive. The process is an extraction process and discloses no provision for adding, for example, a chelating agent, and it is not a two-phase process such as is disclosed herein.
British Pat. No. 1,559,948 (Buckley) teaches a method of recovering heavy oil from tar sand (which is sometimes incorrectly attributed to being equivalent to diatomite). Buckley teaches a method of recovering oil from tar sand in which a steam distillable solvent and an oil soluble surfactant are simultaneously injected. The solvent is variously described as being, for example, kerosene or naphtha. The surfactants are described as being in one of two classes, i.e., thermally labile or steam distillable. An oil soluble surfactant such as thermally labile surfactants are suggested as being alkylaryl sulphonates or alkaryl naphthenic sulphonates. Examples of such steam distillable surfactants are suggested as being alkyl and other amines. Again, this is an extraction process and does not suggest a more preferred two-phase process such as disclosed herein.
It is clear from the above that an improved method of producing oil from diatomaceous formations is desirable.